This invention relates generally to pulsed light sources, and more particularly to an improved high intensity ultraviolet light source for the efficient initiation of pulsed lasers.
The efficient initiation of pulsed lasers, and particularly pulsed chemical lasers such as the HF/DF type, requires an intense ultraviolet light source (about 285 nm), a fast rise time (about 0.5 microsecond), and a pulse width of about one microsecond. Conventional noble gas flashlamps, such as those containing xenon, are operated in a mode dominated by thermal ionization, and have been found to be of marginal utility in meeting the criteria for highly efficient operation since this type of lamp functions substantially as a black body radiator and must be raised to an effective plasma temperature of about 13,000.degree. K. or higher for maximum radiation efficiency. Specifically, for a xenon lamp, a temperature of about 13,365.degree. K. provides a maximum radiation efficiency of about 26.18% through a fused quartz enclosure in the 250 to 400 nm wavelength range. Conventional modes of operation for these lamps, however, typically require several microseconds to achieve an effective temperature of 10,000.degree. K. or higher, the limitation being the rate at which energy can be loaded into the lamp.
The present invention describes an ultraviolet light source and associated circuitry wherein a flashlamp (xenon) is operated in two different modes in achieving the desired temperature in the desirably short time. Specifically, the lamp is initially operated in a streamer mode during the turn-on period for the lamp both for the purpose of generating ultraviolet light and for speeding up the rate at which the bulk temperature of the lamp rises to the level required for the conventional thermal mode of operation. According to the present invention, sufficiently high electric fields are impressed upon the lamp containing a noble gas at low pressure so that both thermal and electric field stress contribute to the ionization, and the lamp will turn on (i.e., raise to sufficiently high effective temperature) much more rapidly. Further, substantial enhancement of ultraviolet radiation centered at about 300 nm occurs when the lamp is driven with electric fields of the order of about 150 Townsends.
It is therefore an object of the present invention to provide a high efficiency pulsed ultraviolet light source.
It is a further object to provide a pulsed ultraviolet light source for the efficient initiation of pulsed lasers.
It is a further object to provide a pulsed ultraviolet light source having rapid rise time and pulse width of one microsecond or less.
These and other objects of the present invention will become apparent as the detailed description of certain representative embodiments thereof proceeds.